Air vehicles require one or more power plants to provide propulsive power and systems power. The power plants can take a variety of forms, including an internal combustion engine. Depending on the type of aircraft being powered, the engine may need to be run, restarted or started at altitudes up to and exceeding 41,000 ft. (1960 m) with ambient temperature conditions down to and below −65° F. At such an altitude and temperature, atmospheric air pressure may be only 20% that of sea level air pressure.
Accordingly, it is necessary to provide an intake for the internal combustion engine that includes an air charge system to increase the mass flow temperature and/or pressure of the intake air to start up internal combustion engines and run them at a steady state condition to produce sufficient power for the vehicle's needs. Such air charge systems typically may include compressors driven by exhaust air (i.e., turbochargers) and compressors driven by motors (i.e., superchargers) and hybrid variations (i.e., turbochargers with integrated motors) in order to increase mass flow rate of ambient air used by the internal combustion engine. Turbochargers have insufficient power available to extract from the exhaust during engine cranking and initial engine run up to provide sufficient boost pressure to the engine to support operation. Mechanically driven superchargers have insufficient speed during engine cranking and initial engine run up to provide sufficient boost pressure to the engine to support operation.
A problem encountered with such air charge systems is that it is difficult to match the engine air mass flow requirements and the volumetric flow consumed by the engine during all modes of operation, namely, start up, run up to steady state operation, steady state operation at prescribed power output levels, transient operation, and shut down. If mass and volume flow of air is not properly matched between the air exiting the compressors and air charging the cylinders of the engine, surging of the compressors may occur, possibly damaging the compressors, or the engine will develop insufficient power.
Air charge systems have been equipped with bleed valves to prevent an overpressure situation from occurring in the air charge system. However, there is a need for an air charge system in which the volumetric flow rate of air delivered to the associated internal combustion engine may be controlled with precision during all modes of engine operation, and at altitude.
An additional problem encountered is that at low ambient temperatures, the fuel vaporization rate will be significantly reduced, resulting in either reduced power output or a lack of detonation of the fuel within the engine. The engine and/or the engine intake air may have insufficient heat to vaporize the fuel, depending on the operating condition of the engine.
If the internal combustion engine is a compression ignition engine, there must be sufficient pressure and temperature generated within the cylinder to support auto ignition. This pressure is dependent on the engine compression ratio, the intake pressure and engine speed. Operation at extreme altitude conditions significantly drops the entrance pressure, creating additional problems.